The engines in Nascar Sprint Cup cars are 90-degree pushrod V8s, just like those that have powered many vehicles on American roads for more than 50 years. But today, the engine under Jimmie Johnson's hood is a custom-made 850-hp 358-cubic-inch thoroughbred that's optimized to run flat-out for no more than 1000 miles. Stock car racing began with slightly modified versions of street-car engines, but over the years the stock car engine has become less and less "stock" as it has used fewer and fewer production car parts.

Some vestiges of the old days remain: For instance, Nascar engines must use a carburetor, pushrods, two valves per cylinder and a wedge-shaped combustion chamber—that's right, no hemis allowed. Nascar found that this formula ensured close-fought competition between a variety of manufacturers and teams, and they have stuck with it even as street cars began to use advanced technology like variable-cam timing and fuel injection. Change is in the air for next season; all Nascar engines will run an electronic fuel-injection system supplied by McLaren Racing. For 2011, though, carburetors still reign.

But while a Nascar engine may look like its showroom counterpart, the wildly different requirements for the two mean that they are built in completely different ways. Race engines have to run at high rpm, producing maximum power for a short time (compared to road cars) and are built with nearly unlimited budgets. Production engines must consider fuel economy, emissions, noise, vibration and harshness levels. Plus, they have to survive on very little maintenance for 150,000 to 300,000 miles, start in minus 20 F weather and cost less than $1500 for the manufacturer to build. These are the biggest differences between what's under Johnson's hood and what's under yours.

1) Valvetrain

Virtually all modern engines operate their valves through one or two overhead camshafts that push the valves open from above. It used to be that a single camshaft mounted in the engine block opened the valves from below, using long pushrods to activate rocker arms that pressed the valves open. This is still how the GM small-block V8 and the Chrysler Hemi V8 operate, though the Hemis splay the valves apart to fit into a pentroof combustion-chamber design (sorry, Chrysler—it isn't really a semihemispherical "hemi" shape anymore, though it's close). But Nascar engines still use the older, less efficient wedge-combustion-chamber shape with the intake and exhaust valves aligned in the same plane.

Those long pushrods aren't ideal for 10,000-rpm operation—the high forces cause the rods to deflect, decreasing valve lift. So, the race engines have cams that are mounted high in the block to shorten the length of the pushrods.

Nascar team owner and renowned engine builder Jack Roush reckons that the metallurgy that permits steel valve springs to survive 10,000-rpm operation could well be the most important bit of technology in these engines. Hard surface coatings such as diamond-like carbon and titanium nitride are critical in helping highly stressed components survive. In production engines, roller tips on the valve lifters help them slide over the cam lobes with minimal friction. But roller lifters aren't permitted in Nascar; instead, the car builders use those surface coatings to help the cam lobes survive a race distance.

2) Induction

All modern automotive engines in the U.S. market employ electronic fuel injection to provide the air–fuel mixture needed for combustion. Nascar engines use the century-old carburetor design to do this, relying on engine vacuum to siphon fuel out of the carb's float bowls through jets of a precise diameter, which determines the air–fuel ratio.

While the design is a venerable one, carburetors have endured so long because they work very well, especially in racing applications where pollution isn't a concern. Carburetors' longevity has allowed a century of continuous refinement. (Even my son might get his homework done in a hundred years.)

"Volumetric efficiency is our number 1 target," Ford Racing engine engineer David Simon says, and carburetors serve that goal well. The relatively poor job the carburetor does distributing fuel equally is less important, and the intake charge cooling that occurs when fuel absorbs heat as it evaporates in the intake manifold is also very helpful.

3) Engine Block

The block in the Sprint Cup car splays the cylinders at 90 degrees, just like in the production V8 that might be under your hood. But this block is designed with significant differences. To start with, the race engine is cast with none of the threaded mounting bosses for attaching accessories or vibration-reducing engine mounts.

And the block itself is designed with lightness in mind, at the expense of long-distance durability. Geometrically, the camshaft sits high in the valley of the V to shorten the length of the pushrods and to leave more space around the crankshaft for air to move freely. The camshaft fits into a cast-in tunnel that separates it from the crankcase to prevent oil from dripping off the cam and onto the crankshaft, according to Simon. "We used to have to do that manually, sealing the cam off with sheet metal," he says.

Even the racing block's material is different. Production blocks, formerly cast iron, are now mostly aluminum to save weight. But Nascar mandates that the race engine block still be made with iron. Race-engine builders comply by using the strongest kind of iron they can—compacted graphite iron.

Because weight is more important than longevity, race engines forego stiffness for mass. As a result, these blocks flex and bend under the stress of their work, according to Patrick Baer, supervisor of Dodge Motorsports engine programs. "Race engines suffer much more deformation than production engines," he says. "They violate every set of design rules you have for production engines. A production engine designer would look at a race engine and say that part will never live. But to make something really stiff, you have to add structure, and structure is weight, and weight is not the friend of the race engine."

4) Lubrication System

In your car's engine, extra oil collects in what is essentially a bucket under the crankcase after it drips off the parts it is lubricating. From there, the oil pump pushes it back up through the passages in the block, and it starts working its way back down again. That's fine for your car, but in a racing engine, all that sloshing oil robs the power that Dale Earnhardt Jr. needs to pass Kyle Busch or Jimmie Johnson.

Racing engines use a dry sump system, which catches oil as soon as it reaches the crankcase. Oil is then sucked out of the engine by the externally mounted pump's scavenge stage and sent to an oil tank. Keeping oil in an external tank allows the whirling and reciprocating parts of the crankcase to move through clean air, boosting power by as much as 10 or 20 horsepower, according to David Currier, vice president of engine engineering for Toyota Racing Development. "If there is less oil in there (the crankcase), there is less change of the parts hitting the oil," he observed. Storing oil in an external tank also keep it cool and gives it a chance to separate out the air bubbles, Currier says.

You know that new, low-viscosity 5W-20 oil carmakers are using now to improve fuel economy? It is molasses compared with the 0W-5 oil Nascar teams use to minimize pumping losses and friction. "It gets to be a bit like water," Currier says. And that thin, runny oil lacks the anti-corrosion additives and detergents that oil in street cars needs to last between oil changes, since race cars get new oil for every race.

5) Reciprocating Parts

Here is where we really see the power of money. Production engines live and die by a couple of dollars, while cost is no object for racing engines. (We've heard that one Nascar engine runs about 50 grand.) The pistons, rings and wrist pins in a Cup engine cost about three times the cost of an entire production Hemi V8, reports Baer.

Then consider NASCAR's exotic (and expensive) titanium valves. The expense comes from the complex shape of the race pistons and the precise machining of their surfaces, Baer says. "You can't just knock them out on a lathe," he said. "It takes special equipment to make them."

The same goes for the crankshaft, which is made of an advanced iron alloy. Even race spark plugs are unorthodox and comparatively pricey, Baer adds. "Production spark plugs cost pennies and ours cost dollars," he says.

The Bottom Line: Why Do It?

Racing improves the breed, the old adage goes. But the stark differences between production and racing engines underscore the unsuitability of technology transfer between the two. What racing truly does, then, is help teach engineers to think creatively, unfettered by the usual limits of production programs. "I don't care how hard it is to machine," Baer tells his engineers. "We can do anything so don't let that influence your decision process."

In addition, Baer says, "one of the positive attributes of racing is the feeling of empowerment people get when they realize they are not being constrained by a manufacturing person or a finance person or a procurement person." So when racing engineers return to work on production programs later, they are in the habit of thinking creatively and unconventionally, he says, which can help produce new solutions even within production constraints.